Acquired equine motor neuron disease (AEMND) is a newly described disease in horse. AEMND is characterized by clinical symptoms of progressive weakness, weight loss, muscle fasiculations, muscle atrophy, and elevated serum creatine phosphokinase. These clinical symptoms coupled with the pathologic depiction of neural degenerative changes are very similar to those described in humans affected with sporadic amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease. Therefore, this study may be used as an animal model for ALS to obtain insight into the etiology, pathogenesis and biochemical mechanisms underlying the human disorders. Previous animal models failed to provide new information to understand ALS because they were either experimental models based on hypothesized etiologic factor or hereditary models that were based on hypotheses which the investigators failed to prove. However, AEMND in horses is advantageous to previous models due to the similarities in clinical signs and pathological lesions between the condition (AEMND) and ALS. We proposed this study to fully describe the distribution of the neurologic changes and determine the rate of occurrence of newly described acquired equine motor neuron disease (AEMND) in horses in the Northeast of the US. We also are planning to identify risk factors associated with this disease and quantifying their risk on the likelihood of developing AEMN. The epidemiologic study of choice is the ambidirectional design. This design, also referred to as nested case- control design, combines elements of cohort and case-control epidemiologic study designs. We will identify the horse population in the Northeast, US and follow them for 5 years. Suspected cases will be examined pathologically for confirmation and additional description of the neurodegenerative changes at New York State College of Veterinary Medicine (NYSCVM). The rate of occurrence of AEMND will then be determined. Noncases (controls) will also be selected from the horse population from which a AEMND case was identified. A comparison between cases and noncases with respect to the putative risk factors will then be made. These risk factors include intrinsic factors (age, sex, breed), health (disease history), management (husbandry, nutrition), and environmental factors (location, toxins, heavy metals, ...etc). Multivariate statistical techniques (logistic regression) will be used to identify risk factors significantly associated with the likelihood of developing AEMND while controlling simultaneously for other possible risk factors.